ACPI / hotplug / PCI: Eliminate acpiphp_dev_to_bridge()

Since acpiphp_dev_to_bridge() is only called by
acpiphp_check_host_bridge(), move the code from it to that function
directly which reduces the call chain depth and makes the code
slightly easier to follow.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>